Config

My first draft for #67 using LLVM's YAML parser.

Here's how the format looks:

<pre>
rules:
  - LongLine
disable-rules:
rulePaths:
  - /etc/rules
rule-configurations:
 - key: LONG_LINE
   value: 20
output: filename
report-type: xml
max-priority-1: 10
max-priority-2: 20
max-priority-3: 30
enable-clang-static-analyzer: false
</pre>

I wish "rule-configurations" would look more like this:
<pre>
LONG_LINE: 20
</pre>
but LLVM's YAML parser doesn't seem to support direct mapping to a map.